1. Field of the Invention
The invention relates to a method of starting to cast a metal strip close to its final dimensions, in which the melt, in particular steel, is led via a melt feed vessel into a pouring chamber of a siphon-like vessel and from this pouring. The invention further relates a casting nozzle via a main chamber which can be put under vacuum, and to a casting nozzle for implementing the method.
2. Discussion of the Prior Art
German references DE 43 44 953 discloses a method, including the device necessary for this, for starting to cast a metal strip close to its final dimensions, in which a shut-off element is provided in the casting nozzle in the vicinity of the opening, with which element the casting nozzle can be shut off and is opened like a slot when starting to cast.
In rough environments, shut-off elements are subjected to extremely high loadings and therefore require intensive maintenance. In addition, qualified operating personnel are needed in order to run the correct program for the slot-like opening in the casting channel.
The object of the present invention is to provide a method with a corresponding device for starting to cast a metal strip close to its final dimensions, which permits the strip casting plant to be started up reliably using a constructionally simple and low-maintenance device.
According to the invention, in the siphon-like vessel, the pouring chamber and therefore the main chamber are filled until the liquid melt flows over the top of the siphon into the casting nozzle. As the melt flows out over the underside of the channel of the casting nozzle, the melt stream is led through the casting nozzle in such a way that its cross section closes in the manner of a plug.
For this purpose, first of all means are provided which deflect the melt stream flowing out two-dimensionally in the form of a ski jump, so that a plug is formed in the casting channel. The deflection can also be brought about by switching on a magnet arranged outside the casting nozzle.
In order to form the plug in the opening area of the casting nozzle, it is proposed to configure the opening in such a way that, essentially by means of a defined spacing of the top of the channel of the casting nozzle, as the melt stream encounters the upper run of the endless belt, it is deflected in such a way that the entire opening briefly fills up with melt and forms a plug.
The plug is maintained by the vacuum produced during the start-up by the vacuum pump connected to the main chamber, and is enlarged by the melt which subsequently flows, a small proportion of the melt being discharged onto the endless belt. After a reliable hydraulic connection in relation to the melt stream has been formed between the inlet into the pouring chamber and the outlet via the opening of the casting channel, the vacuum is adjusted so that the main chamber is adequately supplied with melt and the level in the pouring chamber is kept slightly above the height of the cast strip. After the casting relationships have stabilized, the vacuum device can be switched off, being used only in the event of any leakage. The entire regulation of the melt feed is carried out directly by measuring the level in the pouring chamber or measuring the height of the finished strip.
If an elevated section similar in shape to a ski jump is used on the underside of the channel, this section is configured in such a way that it does not hamper the melt flow during normal operation but effects the reliable formation of a plug at the beginning of casting.
To the extent that the plug is intended to be formed only in the opening area, this is ensured by a predefinable distance of the opening from the top of the channel. In an advantageous refinement, it is proposed to reduce the height by an extension being fitted to the top of the channel, said extension reliably deflecting the impinging melt stream but being consumed by the melt itself during operation.